elseif/else if

(PHP 4, PHP 5, PHP 7)

elseif, as its name suggests, is a combination
of if and else. Like
else, it extends an if
statement to execute a different statement in case the original
if expression evaluates to
FALSE. However, unlike
else, it will execute that alternative
expression only if the elseif conditional
expression evaluates to TRUE. For example, the
following code would display a is bigger than
b, a equal to b
or a is smaller than b:

There may be several elseifs within the same
if statement. The first
elseif expression (if any) that evaluates to
TRUE would be executed. In PHP, you can also
write 'else if' (in two words) and the behavior would be identical
to the one of 'elseif' (in a single word). The syntactic meaning
is slightly different (if you're familiar with C, this is the same
behavior) but the bottom line is that both would result in exactly
the same behavior.

The elseif statement is only executed if the
preceding if expression and any preceding
elseif expressions evaluated to
FALSE, and the current
elseif expression evaluated to
TRUE.

Note:
Note that elseif and else if
will only be considered exactly the same when using curly brackets
as in the above example. When using a colon to define your
if/elseif conditions, you must
not separate else if into two words, or PHP will
fail with a parse error.

User Contributed Notes 6 notes

The parser doesn't handle mixing alternative if syntaxes as reasonably as possible.

The following is illegal (as it should be):

<?if($a): echo $a;else { echo $c;}?>

This is also illegal (as it should be):

<?if($a) { echo $a;}else: echo $c;endif;?>

But since the two alternative if syntaxes are not interchangeable, it's reasonable to expect that the parser wouldn't try matching else statements using one style to if statement using the alternative style. In other words, one would expect that this would work:

<?if($a): echo $a; if($b) { echo $b; }else: echo $c;endif;?>

Instead of concluding that the else statement was intended to match the if($b) statement (and erroring out), the parser could match the else statement to the if($a) statement, which shares its syntax.

While it's understandable that the PHP developers don't consider this a bug, or don't consider it a bug worth their time, jsimlo was right to point out that mixing alternative if syntaxes might lead to unexpected results.